Vehicle communication systems are used in an ever increasing number of vehicle applications and operations, including those pertaining to autonomous and semi-autonomous driving. For instance, many vehicle communication systems include a telematics unit or other type of wireless unit that sends and/or receives data over a cellular network. Most cellular networks support more than one radio access technology (RAT), such as 3G, 4G, LTE, WCDMA, etc., as the large variety of devices within a particular cellular coverage area may require different RATs. Higher-order RATs are usually more prevalent in populous areas, while lower-order RATs are more common in rural areas. Although higher-order RATs may cover less area, they provide faster data transfer and, generally, wireless devices communicating over a cellular network are designed to prefer higher-order RATs when available. This is particularly true when the wireless devices are being used with certain vehicle applications, like those relating to autonomous and semi-autonomous driving, where fast and non-interrupted data transfer over the cellular network is needed.
When a wireless device exits a cellular coverage area of a higher-order RAT, the wireless link is released due to a loss of connection. Most wireless devices are configured to automatically seek and establish connections to lower-order RATs in response to the released wireless link, provided one is available. The converse, however, is not always true. When a wireless device is initially connected via a lower-order RAT and then enters a cellular coverage area also having a higher-order RAT, the wireless link is not released because the lower-order RAT is still available. Cell phones and other personal electronic devices are usually quick to recognize the presence of the higher-order RAT in this situation because they oftentimes are running applications that request data in bursts—a request for data is triggered, for example, via user operation. When the cell phone is not transferring data for a certain amount of time (e.g., in between requests or bursts), there is a natural pause in the data transfer that allows the wireless link with the lower-order RAT to be released in favor of a connection with the higher-order RAT.
The same may not be true, however, for vehicle telematics units and other vehicle wireless devices that require non-interrupted or nearly non-interrupted cellular data transfer for certain operations, like autonomous or semi-autonomous driving operations that rely on GPS/GNSS correction data for precise positioning algorithms. In these situations, there may be no natural pause or break in the data transfer that automatically allows the wireless link with the lower-order RAT to be released and a wireless link with the higher-order RAT to be established. Accordingly, when a vehicle telematics unit engaged in non-interrupted data transfer progresses from a higher-order RAT like 4G to a lower-order RAT like 3G or 2G, the telematics unit may remain in the lower-order RAT for the remainder of the driving session, even if it subsequently reenters a cellular coverage area supporting the higher-order RAT.
The method and system disclosed herein is designed to address such a situation.